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Abstract:

A method for determining interface temperatures for a dry dual clutch
mechanism includes determining that a slipping event is occurring at a
friction interface of a clutch in the dry dual clutch mechanism, and
determining a heat flux generated by the slipping event. The method
includes determining a flux bulk temperature from the determined heat
flux and determining a flux interface temperature from the determined
heat flux. The flux interface temperature is the temperature at the
friction interface during the slipping event. The method calculates a
delta interface temperature by subtracting the flux interface temperature
from the flux bulk temperature. The method executes a control action with
the calculated delta interface temperature.

Claims:

1. A method for determining interface temperatures for a dry dual clutch
mechanism, comprising: determining that a slipping event is occurring at
a friction interface of a clutch in the dry dual clutch mechanism;
determining a heat flux generated by the slipping event; determining a
flux bulk temperature from the determined heat flux; determining a flux
interface temperature from the determined heat flux, wherein the flux
interface temperature is the temperature at the friction interface;
subtracting the flux interface temperature from the flux bulk temperature
to calculate a delta interface temperature; and executing a control
action using the calculated delta interface temperature.

2. The method of claim 1, further comprising: reading an absolute bulk
temperature; adding the delta interface temperature to the absolute bulk
temperature to calculate an absolute interface temperature.

3. The method of claim 2, further comprising: determining a coefficient
of friction for the clutch in the slipping event, wherein the coefficient
of friction is a function of the calculated absolute interface
temperature.

4. The method of claim 3, further comprising: storing the absolute
interface temperature; calculating one of a maintenance interval and a
lifecycle of the clutch based upon the absolute interface temperature.

5. A method for determining interface temperatures for a dry dual clutch
mechanism, comprising: determining that a slipping event is occurring at
a friction interface of a clutch in the dry dual clutch mechanism;
determining a heat flux generated by the slipping event, wherein the
method ignores convection to or from the clutch; determining a flux bulk
temperature from the determined heat flux; determining a flux interface
temperature from the determined heat flux, wherein the flux interface
temperature is the temperature at the friction interface; subtracting the
flux interface temperature from the flux bulk temperature to calculate a
delta interface temperature; reading an absolute bulk temperature; adding
the delta interface temperature to the absolute bulk temperature to
calculate an absolute interface temperature; and executing a control
action with the calculated delta interface temperature.

Description:

[0002] Motorized vehicles use dual clutch transmissions to combine some of
the features of both manual and automatic transmissions. Dual clutch
transmissions use two clutches to shift between sets of gears within the
same transmission, operating with some of the characteristics of both
manual and conventional automatic transmissions. Some dual clutch
transmissions use oil-bathed wet multi-plate clutches, and some use dry
clutches without oil or fluid.

SUMMARY

[0003] A method for determining interface temperatures for a dry dual
clutch mechanism is provided. The method includes determining that a
slipping event is occurring at a friction interface of a clutch in the
dry dual clutch mechanism, and determining a heat flux generated by the
slipping event. The method also includes determining a flux bulk
temperature from the determined heat flux and determining a flux
interface temperature from the determined heat flux. The flux interface
temperature is the temperature at the friction interface during the
slipping event.

[0004] The method calculates a delta interface temperature by subtracting
the flux interface temperature from the flux bulk temperature. The method
executes a control action with the calculated delta interface
temperature.

[0005] The above features and advantages, and other features and
advantages, of the present invention are readily apparent from the
following detailed description of some of the best modes and other
embodiments for carrying out the invention, as defined in the appended
claims, when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a schematic plane intersection view of a powertrain
having an illustrative dry dual clutch transmission usable with thermal
models described herein;

[0007] FIG. 2 is a schematic flow chart of a method or algorithm for
determining clutch temperatures in a dry dual clutch transmission, such
as that shown in FIG. 1;

[0009] FIG. 4 is a close up portion of a second clutch from the dry dual
clutch transmission shown in FIG. 1; and

[0010] FIG. 5 is a schematic flow chart of a method or algorithm for
determining interface temperatures of clutches in a dry dual clutch
transmission, such as that shown in FIG. 1.

DETAILED DESCRIPTION

[0011] Referring to the drawings, wherein like reference numbers
correspond to like or similar components whenever possible throughout the
several figures, there is shown in FIG. 1 a schematic diagram of a
powertrain 100. The powertrain 100 may be incorporated into a hybrid
vehicle (not shown) or a conventional vehicle (not shown). Features,
components, or methods shown or described in other figures may be
incorporated and used with those shown in FIG. 1.

[0012] While the present invention is described in detail with respect to
automotive applications, those skilled in the art will recognize the
broader applicability of the invention. Those having ordinary skill in
the art will recognize that terms such as "above," "below," "upward,"
"downward," et cetera, are used descriptively of the figures, and do not
represent limitations on the scope of the invention, as defined by the
appended claims.

[0013] The powertrain 100 includes a dry dual clutch transmission 110,
which may be referred to herein as the dry DCT 110 and receives power
from an internal combustion engine 112. The dry DCT 110 includes a
transmission gearbox 114 and dual clutch mechanism 116. The engine 112 is
drivingly connected for powerflow communication with the dry DCT 110. The
dual clutch mechanism 116 selectively allows torque transfer between the
engine 112 and the gearbox 114.

[0014] The gearbox 114 is operatively connected to a final drive 118 (or
driveline). The final drive 118 is shown schematically and may include a
front or rear differential, or other torque-transmitting mechanism, which
eventually provides torque output to one or more wheels (not shown). The
final drive 118 may include any known configuration, including
front-wheel drive (FWD), rear-wheel drive (RWD), four-wheel drive (4WD),
or all-wheel drive (AWD), without altering the description herein.

[0015] Only a portion of the powertrain 100 is illustrated in FIG. 1. The
lower half (as viewed in FIG. 1) of the powertrain 100 is below a central
axis 120, but may be substantially similar to the portions shown. The
transfer shafts between the dual clutch mechanism 116 and the engine 112
and gearbox 114 are not shown in FIG. 1. The dual clutch mechanism 116 is
housed in a bell housing or bell housing case 122.

[0016] The dual clutch mechanism 116 includes a first clutch 132 or clutch
one (C1) and a second clutch 134 or clutch two (C2). A center plate 136
(CP) is between the first clutch 132 and the second clutch 134. Each of
the first clutch 132 and the second clutch 134 includes friction discs,
friction plates, or other friction materials. The center plate 136
contains corresponding friction plates.

[0017] A first friction interface 142 at the friction plates between the
first clutch 132 and the center plate 136. When the dual clutch mechanism
116 is allowing slip (relative difference in rotational speed) and
transferring torque between the first clutch 132 and the center plate
136, the first friction interface 142 generates heat. A second friction
interface 144 at the friction plates between the second clutch 134 and
the center plate 136. When the dual clutch mechanism 116 is allowing slip
and transferring torque between the second clutch 134 and the center
plate 136, the second friction interface 144 generates heat.

[0018] A first pull cover 146 and a second pull cover 148 (PC1 and PC2,
respectively) are operatively connected to the first clutch 132 and the
second clutch 134. The first pull cover 146 and the second pull cover 148
are used to actuate torque transfer between the first clutch 132 and the
center plate 136 and between the second clutch 134 and the center plate
136 in order to selectively control power transfer to the gearbox 114.

[0019] The dry DCT 110, and the dual clutch mechanism 116, may be
controlled and monitored by a controller or control system (not shown).
The control system may include one or more components with a storage
medium and a suitable amount of programmable memory, which are capable of
storing and executing one or more algorithms or methods to effect control
of the dry DCT 110 or the powertrain 100. Each component of the control
system may include distributed controller architecture, such as a
microprocessor-based electronic control unit (ECU). Additional modules or
processors may be present within the control system. The control system
may alternatively be referred to as a transmission control processor
(TCM).

[0020] The interior chamber of the bell housing case 122 is filled with
housing air 150. Depending upon the configuration of the dual clutch
mechanism 116 and the thermal model applied used to determine
temperatures of the dual clutch mechanism 116, the powertrain 100 may
include a housing air sensor 152.

[0021] The housing air sensor 152 measures the temperature of air within
the bell housing case 122. The powertrain may also include an ambient air
sensor 154, an engine coolant sensor 156, and a gearbox oil sensor 158.
As used herein, ambient air refers to the air just outside of the bell
housing case 122. The temperature measurements from these sensors may be
used in thermal models to determine the temperatures of the components of
the dual clutch mechanism 116.

[0022] In the dual clutch mechanism 116, there is a critical temperature
of the friction surfaces that carry torque for the first clutch 132 and
the second clutch 134. Above this temperature, the components may start
to suffer permanent damage. Furthermore, the clutch friction
characteristics--i.e., the coefficient of friction and the torque
carrying capacity of the first clutch 132 and the second clutch 134--are
a function of the temperatures of the first friction interface 142 and
the second friction interface 144.

[0023] In many configurations of the dry DCT 110, it may be difficult to
place a temperature sensor directly on the first clutch 132 and the
second clutch 134, and may be impossible to place a temperature sensor
near the first friction interface 142 and the second friction interface
144 of the dual clutch mechanism 116. Therefore, the control system uses
a thermal model to determine the temperatures of the first clutch 132 and
the second clutch 134, to estimate the torque capacity at the first
friction interface 142 and the second friction interface 144, and also to
provide driver warnings to prevent misuse of the dry DCT 110.

[0024] A seven-state thermal model may be used to determine the
temperatures of the first clutch 132 and the second clutch 134 for the
dry DCT 110. However, in some configurations, a simplified, five-state
thermal model may be used instead. The five-state thermal model requires
less computational throughput.

[0025] When the seven-state thermal model is used, the states (or
temperatures) are calculated at: the first clutch 132, the second clutch
134, the center plate 136, the first pull cover 146, the second pull
cover 148, the bell housing case 122, and the housing air 150. When the
simplified, five-state thermal model is used, the states are reduced to:
the first clutch 132, the second clutch 134, the center plate 136, the
first pull cover 146, and the second pull cover 148. The five-state
thermal model may be used when the temperature of the housing air 150 is
know, such as from the inclusion of the housing air sensor 152.

[0026] The five-state thermal model will be described first. When either
the first clutch 132 or the second clutch 134 is applied, the apply force
pushes the corresponding pressure plate of the first clutch 132 or the
second clutch 134, squeezing the friction discs against the center plate
136. The dual clutch mechanism 116 is encased in the bell housing case
122, which is assembled between the engine 112 and the gearbox 114. The
first clutch 132, the second clutch 134, the center plate 136, the first
pull cover 146, and the second pull cover 148 are all masses that conduct
heat, and each mass in the system is represented by a single temperature
state.

[0027] The bell housing case 122 has no forced cooling and has no vents.
The heat from the masses is transferred by convection to the housing air
150 and from the housing air 150 to the bell housing case 122 mass. Heat
is then convected from the bell housing case 122 to the ambient air just
outside of the bell housing case 122.

[0028] There is also heat transfer between the bell housing case 122 and
the engine 112 the gearbox 114. However, it is assumed that heat from the
masses is transferred only to bell housing air 150. Therefore, when the
housing air sensor 152 provides known temperatures of the housing air
150, the five-state thermal model is configured to use state equations
representing the temperature of the masses. The five-state thermal model
also assumes that other heat sources, such as the engine 112, the gearbox
114, and the ambient air, will not separately affect the temperature
prediction beyond the measured temperature of the housing air 150.

[0029] The governing equation describing the heat balance for each
individual mass is given by:

Massi*Cpi*dTi=Qi--in-Qi--ou-
t

where Massi and Cpi represent the mass and specific heat of the
specific component of the dual clutch mechanism 116 under consideration;
Qi--in and Qi--out represent the heat input
and heat output for the mass, respectively; and dTi is the change in
mass temperature with respect to time.

[0030] When either the first clutch 132 or the second clutch 134 is
applied and torque is transmitted across the clutch, heat is generated at
the first friction interface 142 or the second friction interface 144 is
if the applied clutch is slipping. When there is no slip, the two sides
of the clutch are rotating substantially in sync and substantially all
power is transferred through the clutch.

[0031] Using the first clutch 132 for illustration, the five-state thermal
model assumes that the heat generated at first friction interface 142 is
absorbed by substantially equally by the first clutch 132 and center
plate 136. The temperatures of the first clutch 132 and center plate 136
increase during the slip event, resulting in heat transfer due to
conduction and convection to other components in the dual clutch
mechanism 116.

[0032] Because the equations are similar for all of the masses used in the
five-state and the seven-state thermal models, only the equations for the
first clutch 132 are illustrated here. The heat power input (Watts) to
the first clutch 132 is the product of torque (Nm) and slip speed (rad/s)
at the first clutch 132. The heat power integrated over time results in
heat (joules).

[0033] The slip speed is known or may be determined from measurements or
estimates of input speeds and output speeds of the dual clutch mechanism
116 or the dry DCT 110. Similarly, the torque carried by the first clutch
132 is known or determined from torque of the engine 112 or other
parameters.

[0034] The discrete form of the heating mode of the first clutch 132 is
given by:

where Cpc1 is the specific heat of the material of the first clutch
132 and Massc1 is the mass of the first clutch 132. The term k
represents the value of the variable (such as temperature of the first
clutch 132) at time k and is the instant (or current) time period or loop
of the thermal model. The term k+1 represents the next time period, after
the lapse of delta_time.

[0035] The heat losses due to conduction from the first clutch 132 to the
first pulling cover 146 and to the center plate 136 are given by the
following expressions:

Heatloss--PC1=[Tc1(k)-Tpc1(k)]*Cond*Area--PC1

Heatloss--CP=[Tc1(k)-Tcp(k)]*Cond*Area--CP

where Cond is the thermal conductivity of the connecting material.
Area_PC1 and Area_CP are the conducting areas divided by the thickness of
the conducting sections. The area/thickness values for each conduction
path may be identified by testing and data optimization or by CAD models.
These heat losses are subtracted from the heat input due to the slippage
at the first friction interface 142.

[0036] The cooling of the first clutch 132 due to convection is given by:

Tcc1(k+1)=(Tc1(k)-Thousing(k))*exp(-b*
delta_time)+Thousing(k)

where Thousing is the measured housing air temperature and b is the
cooling coefficient for the first clutch 132.

[0037] The cooling coefficient is given by:

b=hc1*Ac1/(Cpc1*Massc1)

where Ac1 is the surface area of the first clutch 132 that is
convecting the heat and hc1 is the heat transfer coefficient.

[0038] The heat transfer coefficient is calculated using the Nusselt
number. The Nusselt number is proportional to the square root of the
Reynold's number, with the proportionality constant, NuReConstc1, to
be determined from the cooling data for the first clutch 132. The
Reynolds number is function of clutch speed, as shown in the equations
below:

hc1=Nu*Kair/mean_radius

Nu=NuReConstc1*sqrt(Re)

Re=ωc1*mean_radius2/(mu/rho)

where mu is the viscosity of air, rho is the density of air, Kair is
the conductivity in air, and the mean_radius is of the first clutch 132.
Similar equations can be derived for the other four masses (the second
clutch 134, the center plate 136, the first pull cover 146, and the
second pull cover 148) in the dual clutch mechanism 116.

[0039] With similar equations for all five of the masses in the dual
clutch mechanism 116, the control system determines the operating
temperature of any of the individual components due to heating during
slip events (usually from gear changes or launches) and cooling during
non-slip events (steady state operations). The goal, or target, of the
five-state thermal model is to determine the temperature of the first
clutch 132 and the second clutch 134. These temperatures may be referred
to as the bulk temperatures of the first clutch 132 and the second clutch
134 and represent average temperature throughout the whole mass of the
component. From the bulk temperatures, the control system can determine
whether the first clutch 132 and the second clutch 134 are below critical
temperatures and estimate the torque capacity at the first friction
interface 142 and the second friction interface 144.

[0040] Some of the inputs and values of the heating and cooling equations
may not be easily determined through inspection, reference tables, or CAD
models. These inputs and values may be determined through data
optimization by comparing testing data of the dual clutch mechanism 16
with pre-optimized simulations. The data is optimized by comparing the
simulations with the test data, and the five-state thermal model is
developed with more-precise inputs and values for the actual dual clutch
mechanism 116 used.

[0041] The five-state thermal model is developed to determine temperatures
of the first clutch 132 and the second clutch 134 based upon heating
events (clutch slipping) and cooling events (periods of non-slipping
engagement or non-engagement). The five-state thermal model may be
running within the control system at all times, including during vehicle
off periods. In such a case, the five-state thermal model tracks all
changes to the temperature of the first clutch 132 and the second clutch
134, and the temperatures are accurate absolute temperatures.

[0042] However, if the five-state thermal model is not running while the
vehicle is turned off or in shut-down mode, the five-state thermal model
will actually be determining the changes to temperatures of the first
clutch 132 and the second clutch 134. Therefore, the control system may
also need to know the initial (starting) temperatures of the first clutch
132 and the second clutch 134 at vehicle start-up in order to determine
the absolute temperatures from the temperature changes (delta
temperature) determined by the five-state thermal model. Vehicle start-up
and vehicle shut-down states may be defined in numerous ways or may be
based upon the running state of the engine 112. The initial temperatures
may be separately determined by the control system--such as from another
model.

[0043] The five-state thermal model operates with known temperatures from
the housing air 150, such as from the housing air sensor 152. However, it
may not always be practical or possible to have the housing air sensor
152 or another mechanism for determining the temperature of the housing
air 150. Without known housing air 150 temperatures, the five-state
thermal model may be insufficient to determine the temperature of the
first clutch 132 and the second clutch 134. Therefore, the non-simplified
model, the seven-state thermal model, is used to determine the
temperature of the first clutch 132 and the second clutch 134 when the
temperature of the housing air 150 is not known or readily determined.

[0044] The seven-state thermal model includes temperature states or nodes
for the bell housing case 122 and for the housing air 150 contained
therein. The five-state thermal model included only two heat sources, the
heat generated during slip events at the first friction interface 142 and
the second friction interface 144 of the first clutch 132 and the second
clutch 134, respectively. However, the dual clutch mechanism 116 is also
in heat-exchange communication with the engine 112, the gearbox 114, and
the ambient air outside of the bell housing case 122. The effects of
these other heating or cooling sources are actually incorporated into the
five-state thermal model through the known temperature of the housing air
150. Since the seven-state thermal model does not include known
temperatures of the housing air 150, the heat effects of the engine 112,
the gearbox 114, and the ambient air are incorporated into the
seven-state thermal model.

[0045] When the seven-state thermal model is used, the powertrain 100 is
equipped with mechanisms to determine the temperature of the engine 112,
the gearbox 114, and the ambient air outside of the bell housing case
122. As illustrated in FIG. 1, the engine coolant sensor 156, the gearbox
oil sensor 158, and the ambient air sensor 154 may determine these
temperatures for used in the seven-state thermal model. Alternatively,
especially for the ambient temperature, other sensors may be used to
closely approximate the temperature. For example, a sensor may be located
at the air intake for the engine 112, and this temperature may be used as
the ambient air temperature for the seven-state thermal model, instead of
locating the ambient air sensor 154 just outside of the bell housing case
122.

[0046] The two additional temperature states and the three additional
heating and cooling sources are replacements in the seven-state thermal
model for the known temperature of the housing air 150 in the five-state
thermal model. Therefore, the five-state thermal model is a simplified
version of the seven-state thermal model. The seven-state thermal model
includes only conduction heat transfer with the engine 112 and the
gearbox 114, with convention and radiation from those sources assumed to
be negligible.

[0047] The equations for the housing air 150 temperature and bell housing
case 122 case temperature can be written as follows. For the housing air
150:

Massh*Cph*dTh=Qh--in-Qh--ou-
t

where subscript h refers to housing air 150 and dTh is the change in
air temperature with respect to time. Qh--in is the amount
of heat convected from the five masses in the dual clutch mechanism 116.
The expressions for Qh--in was given in the description of
the five-state thermal model. Qh--out is the amount of
heat convected to the bell housing case 122 and is given by:

Qh--out=hair*Areaair(Th(k)-Tc(k))

where hair and Areaair are heat transfer coefficient and area
of convection and these are determined by the parameter optimization
tool.

[0048] Similarly, for the bell housing case 122:

Massc*Cpc*dTc=Qc--in-Qc--ou-
t

where subscript c refers to bell housing case and dTc is the change
in temperature of the bell housing case 122 with respect to time.
Qc--in is the amount of heat convected from housing air
150 (Qh-out, given above) and the heat conducted from the engine 112
and gearbox 114 sides.

[0049] Focusing only on the conduction from engine 112 and gearbox 114 to
the bell housing case 122, we can write:

Qeng--gear=Kc*Areaeng(Teng(k)-Tc(k))+-
Kc*Areagear(Tgear(k)-Tc(k))

where Teng is the temperature of the coolant in engine 122, as
measured by engine coolant sensor 156, and Tgear is the temperature
of oil in the gearbox 114, and measured by gearbox oil sensor 158. The
areas of conduction, Areaeng and Areagear, may be very complex
due to the odd shapes and interfaces of the components. Therefore the
areas of conduction may be determined for any specific powertrain 100 by
the parameter optimization from test data.

[0050] The value Qc--out is the amount of heat conducted to
the ambient air just outside of the bell housing case 122, and is given
by:

Qc--out=Kc* Areac(Tc(k)-Tamb(k))

where Areac is the area of convection of the bell housing case 122
and may also be determined by the parameter optimization. Tamb(k) is
the ambient temperature around the bell housing case 122. This
temperature might be different from the temperature outside the vehicle.
The intake air temperature of the engine 112 may be substituted for the
ambient temperature.

[0051] Therefore, the convention and conduction for each of the seven
components in the seven-state thermal model can be determined. The
seven-state thermal model is developed with a lumped parameter approach,
where each component is represented by one temperature state. After
implementation for the specific vehicle and powertrain 100, the control
system uses the seven-state thermal model to determine the bulk
temperatures of the first clutch 132 and the second clutch 134.

[0052] The seven-state thermal model may not be running while the vehicle
is turned off or in shut-down mode, such that the seven-state thermal
model is actually determining the changes to temperatures--as opposed to
the absolute temperatures--of the first clutch 132 and the second clutch
134. Therefore, the control system may also need to know the initial
(starting) temperatures of the first clutch 132 and the second clutch 134
at vehicle start-up in order to determine the absolute temperatures from
the temperature changes (delta temperature) determined by the seven-state
thermal model.

[0053] Referring now to FIG. 2, and with continued reference to FIG. 1,
there is shown a schematic flow chart diagram of an algorithm or method
200 for determining clutch temperatures in a dry dual clutch
transmission, such as the dry DCT 110 shown in FIG. 1. FIG. 2 shows only
a high-level diagram of the method 200. The exact order of the steps of
the algorithm or method 200 shown in FIG. 2 is not required. Steps may be
reordered, steps may be omitted, and additional steps may be included.
Furthermore, the method 200 may be a portion or sub-routine of another
algorithm or method.

[0054] For illustrative purposes, the method 200 may be described with
reference to the elements and components shown and described in relation
to FIG. 1 and may be executed by the control system. However, other
components may be used to practice the method 200 and the invention
defined in the appended claims. Any of the steps may be executed by
multiple components within the control system.

[0055] Step 210: Start.

[0056] The method 200 may begin at a start or initialization step, during
which time the method 200 is monitoring operating conditions of the
vehicle and of the powertrain 100. Initiation may occur, for example, in
response to the vehicle operator inserting the ignition key or in
response to other specific conditions being met. The method 200 may be
running constantly or looping iteratively whenever the vehicle is in use.

[0057] Step 212: Read Previous States (Temperatures).

[0058] The method 200 reads the previous five or seven temperature states.
The previous states are stored by the control system from the last loop
of the method 200. If the method 200 is running for the first time, such
as after the engine 112 and the vehicle have just started, the previous
states may be replaced by initial conditions of the components. If
needed, the initial conditions may be either calculated or estimated by
the control system.

[0059] Step 214: Determine Heat from Clutches.

[0060] The method 200 determines the heat being generated by the clutches.
The heat generated is a function of torque capacity and slip speed of the
first clutch 132 and the second clutch 134. The heat is generated at the
first friction interface 142 and the second friction interface 144.

[0061] When neither the first clutch 132 nor the second clutch 134 is
slipping, such as during steady state operation, no heat is generated by
the clutches. Generally, when no heat is generated by the clutches, the
dual clutch mechanism 116 is cooling.

[0062] Step 216: Determine Housing Air Temperature.

[0063] The method 200 takes the temperature of the housing air 150 into
account regardless of the thermal model being used. If the temperature of
the housing air 150 is known, such as from the housing air sensor 152,
then the five-state thermal model may be used, and the method 200 simply
takes the known temperature from the housing air sensor 152. However, if
the temperature of the housing air 150 is not known, then method 200 uses
the seven-state thermal model instead of directly measuring the
temperature of the housing air 150.

[0064] Step 218: Determine Ambient, Engine, and Gearbox Temperatures.

[0065] If the method 200 is using the seven-state thermal model, steps 218
and 220 are also executed. The method 200 determines or measures the
temperatures of the ambient air outside of the bell housing case 122, the
engine 112, and the gearbox 114. The ambient air sensor 154, the engine
coolant sensor 156, and the gearbox oil sensor 158, respectively, may
measure these temperatures. Alternatively, the temperatures may be
derived or approximated from other known conditions.

[0066] Step 220: Determine Heat from Ambient, Engine, and Gearbox.

[0067] The method 200 calculates the heat transfer between the bell
housing case 122 and the ambient air outside of the bell housing case
122, the engine 112, and the gearbox 114. Depending upon the relative
temperatures involved, heat may be flowing into or out of the bell
housing case 122.

[0068] Step 222: Load Model Parameters.

[0069] The method 200 loads the parameters of the dual clutch mechanism
116 for use with the five-state or seven-state thermal model. The
parameters include, without limitation: heat transfer coefficients and
other characteristics of the specific materials making up the components,
Nusselt and Reynolds numbers for the components experiencing convection,
and the areas and thickness of conduction interfaces between components.

[0070] Step 224: Apply Five-State or Seven-State Thermal Model.

[0071] The method 200 applies one of the thermal models. If the
temperature of the housing air 150 is known, the method 200 applies the
five-state thermal model and includes temperature states for: the first
clutch 132, the second clutch 134, the center plate 136, the first pull
cover 146, and the second pull cover 148. When the temperature of the
housing air 150 is not known, the method 200 applies the seven-state
thermal model and further includes temperature states for the bell
housing case 122 and the housing air 150.

[0072] Step 226: Output Bulk Temperature of Clutches C1 and C2.

[0073] From the thermal model, the method 200 determines the temperatures
of the first clutch 132 and the second clutch 134. These temperatures may
be the primary goal of the method and the five-state or seven-state
thermal model.

[0074] The temperatures of the first clutch 132 and the second clutch 134
may be compared to the critical temperatures for the friction linings of
the first clutch 132 and the second clutch 134 and to alert the driver of
possible damaging conditions. Furthermore, the temperatures of the first
clutch 132 and the second clutch 134 may be used to calculate the
coefficient of friction of the first friction interface 142 and the
second friction interface 144.

[0075] Step 228: Execute Control Action.

[0076] The method 200 executes a control action based upon, at least, the
determined temperatures of the first clutch 132 and the second clutch
134. Executing the control action may include many tasks or operations.

[0077] For example, the control action may include storing all (five or
seven) of the determined temperatures. The stored temperatures may be
used during the next loop, or may be stored as the last conditions when
the vehicle or the engine 112 is turned off.

[0078] Executing the control action may include determining the actual
coefficient of friction at the first fiction interface 142 and the second
friction interface 144 based upon the determined temperatures of the
first clutch 132 and the second clutch 134. The control action may also
include storing the temperatures for calculation of maintenance or
service actions and timelines for the first clutch 132 and the second
clutch 134 or other portions of the powertrain 100.

[0079] Step 230: Stop/Loop.

[0080] The method 200 may stop running until called to run again by the
control system, such as due to occurrence of events likely to change the
temperature of components of the dual clutch mechanisms 116.
Alternatively, the method 200 may run with a scheduled number of loops
per time segment, such as several times per second.

[0081] Referring now to FIG. 3, and with continued reference to FIGS. 1-2,
there are shown schematic charts or graphs that broadly illustrate
testing and validation of the thermal models described herein. FIG. 3
shows actual test data compared with actual data from the five-state
thermal model. During the test, the first clutch 132 was used for
repeated launches from 0 to 1200 rpm slip speed, and then allowed to
cool.

[0082] In the test shown in FIG. 3, the temperatures of the first clutch
132, the second clutch 134, and the center plate 136 were actually
measured. The results of the five-state thermal model with optimized
parameters where also calculated.

[0083] A chart 310 shows the temperature of the first clutch 132, with
temperature shown on a y-axis 312 and time on an x-axis 314. A measured
temperature of the first clutch 132 is shown as a solid line 320. The
upward spikes in the line 320 are increases in temperature due to the
heat created as the first clutch 132 slips from non-engagement to
complete engagement during the launch events. A simulated temperature
from the five-state thermal model is shown as a dashed line 322.

[0084] A chart 330 shows the temperature of the second clutch 134, with
temperature shown on a y-axis 332 and time on an x-axis 334. A measured
temperature of the second clutch 134 is shown as a solid line 340. A
simulated temperature of the second clutch 134 from the five-state
thermal model is shown as a dashed line 342.

[0085] A chart 350 shows the temperature of the center plate 136, with
temperature shown on a y-axis 352 and time on an x-axis 354. A measured
temperature of the center plate 136 is shown as a solid line 360. A
simulated temperature of the center plate 136 from the five-state thermal
model is shown as a dashed line 362. The upward spikes in the line 360
are increases in temperature due to the heat created in the first clutch
132 and passed into the center plate 136 from the first friction
interface 142.

[0086] As shown in FIG. 3, the five-state thermal model closely predicts
the temperatures of the first clutch 132 during the test shown. The
five-state thermal model also closely predicts the temperature of the
second clutch 134 and the center plate 136.

[0087] Referring now to FIG. 4, and with continued reference to FIGS. 1-3,
there is shown a portion of the second clutch 134. The second clutch 134
is schematically illustrated during a heating event caused by slipping
engagement of with the center plate 136 (not shown in FIG. 4).

[0088] Heat is generated during the slipping engagement at the second
friction interface 144 as the friction plates of the second clutch 134
and the center plate 136 slide over each other. The amount of heat
generated is a function of the slip speed and the torque capacity of the
second clutch 134. An interface temperature model is used to determine
the temperature of the second clutch 134 at the friction interface 144,
as opposed to the bulk temperature of the second clutch 134 determined by
the five-state or the seven-state thermal model.

[0089] The coefficient of friction between the second clutch 134 and the
center plate 136 is a function of the interface temperature--i.e., the
temperature at the second friction interface 144. However, the five-state
and the seven-state thermal models calculate the bulk temperature of the
second clutch 134. The coefficient of friction alters the operating
characteristics of the second clutch 134 and changes the way the control
system uses the second clutch 134 to, among other things, launch the
vehicle and change gears in the dry DCT 110.

[0090] While the bulk temperature from the thermal models may be used to
approximate the temperature of the second friction interface 144, and
therefore the coefficient of friction, the control system can better
operate the dual clutch mechanism 116 if the temperature of the second
friction interface 144 is directly determined. Similarly, the temperature
at the first friction interface 142 controls the coefficient of friction
between the first clutch 132 and the center plate 136.

[0091] As shown in FIG. 4, the interface temperature model divides the
second clutch 134 into a plurality of grid portions 135 (six, in the
illustration shown). Each of the grid portions 135 is bounded by a grid
point or node, which are labeled 1 through 7, from right to left, as
viewed in FIG. 4. There is one grid point on each of the two boundaries
or edges of the plurality of grid portions 135.

[0092] For the interface temperature model, the heat transferred to the
second clutch 134 is illustrated schematically as a heat flux 145 applied
at the second friction interface 144. The interface temperature model
uses this one-dimensional heat flux 145 to model the heat input generated
by slipping engagement of the second clutch 134 with the center plate
136.

[0093] The magnitude of the heat flux 145 is a function of the torque
carried by the second clutch 134 and the slip speed across the second
clutch 134. The total heat generated is given by the equation:

Qh=(Torquec2*ωc2--Slip*delta_time)

where Torquec2is the torque carried across the second clutch 134,
and ωc2--Slip is the slip speed of the second clutch
134. Note that the slip speed and the torque carried by the second clutch
134 may be changing throughout the slipping event, so the initial
temperature model may be calculating the heat flux 154 repeatedly or may
be estimating the heat flux 154 as an average during the whole slipping
event.

[0094] The magnitude of the heat flux 154 to the second clutch 134, which
will be denoted qc2, is determined by the interface temperature
model as the one-half the total heat, Qh, spread over the area of
the second clutch 134, such that qc2=Qh/2/dt/area. The other
half of the total heat is transferred to the center plate 136.

[0095] The interface temperature model calculates the temperatures of each
of the grid points during the heating event while the heat flux 154 is
applied. The interface temperature model assumes that no cooling occurs
during this calculation, which takes place over a short duration.
Therefore, the effects of convention to the housing air 150 and
conduction to the second pull cover 148 are not incorporated into the
interface temperature model.

[0096] The remaining heat transfer in the second clutch 134 as a result of
the heat flux 145 is calculated due to conduction between the grid
portions 135. From the conduction equations, the interface temperature
model establishes a one-dimensional, unsteady-state problem, using the
seven grid points.

[0097] The equations for solving for gradient based upon the heat flux 154
from slipping events include separate equations for: the interface
boundary (at grid point 1) at the second friction interface 144; the
outer boundary (at grid point 7) where the second clutch 134 meets the
housing air 150; and the grid portions 135 (between grid points 1 through
2). The interface boundary equation is:

qc2-k/dx*(T1-T2)=(Rho*Cp/dt*dx/2)*(T1-T10)

where k is the conductivity of the material of the second clutch 134, dx
is the width of the grid portions 135 (in this example, one-sixth of the
width of the second clutch 134), T1 and T2 are the temperatures
to be determined at the grid points 1 and 2. Rho is the density of the
material, Cp is the specific heat, the T10 was the previous
temperature (previous time step) of the second friction interface (grid
point 1), and dt is the change in time from the previous iteration. The
interface temperature model may be calculating the temperatures on a
fixed cycle or looping at a fixed interval whenever the dual clutch
mechanism 116 is undergoing slipping events.

[0098] Because there is no cooling to the housing air from the outside
boundary at grid point 7, the outside boundary equation is:

k/dx*(T6-T7)=(Rho*Cp/dt*dx/2)*(T7-T70)

where T6 and T7 are the temperatures to be determined at the
grid points 6 and 7, and T70 was the previous temperature
(previous time step) of the outside boundary (grid point 7). The previous
temperatures may be read from memory of the control system.

[0099] The equations for the other grid points are all substantially
identical to each other, with the exception of the changing points. The
equation for heat transfer at the grid point 2 is:

k/dx*(T1-T2)-k/dx*(T2-T3)=(Rho*Cp/dt*dx/2)*(T2--
T20)

and the equations for grid points 3 through 6 are the same and will not
be separately.

[0100] From the above equations, the solutions for the temperatures
(T1 through T7) at each of the grid points is obtained by a
TriDiagonal Matrix Algorithm (TDMA). The temperature (T1) is a flux
interface temperature, which is the temperature at the second friction
interface 144 calculated by the interface temperature model. The flux
interface temperature may be used to determine the coefficient of
friction or to determine whether any damage to the friction surfaces has
occurred. The interface temperature model also determines a flux bulk
temperature, which is the average of the temperatures of all seven grid
points as a result of the heat flux 154.

[0101] However, the flux interface temperature determined above is
actually only the interface temperature occurring as a result of the heat
flux 154 during the heating event. This flux interface temperature does
not incorporate temperature changes due to previous slipping events and
periods of cooling. For example, the second clutch 134 may be commanded
to slip during a vehicle launch event and then commanded to slip again
during a subsequent shift shortly after the launch event.

[0102] Therefore, the interface temperature model also determines a delta
interface temperature, which is the difference between the flux interface
temperature (point 1) and the flux bulk temperature (average of all
points). The delta interface temperature may be added to the absolute
bulk temperature determined by the five-state thermal model or the
seven-state thermal model--both of which account for previous events and
continually track conditions--to determine the absolute, or real,
interface temperature at the second friction interface 144.

[0103] Referring now to FIG. 5, and with continued reference to FIGS. 1-4,
there is shown a schematic flow chart diagram of an algorithm or method
500 for determining interface temperatures in a dry dual clutch
transmission, such as the dry DCT 110 shown in FIG. 1. FIG. 5 may be a
sub-process or an add-on process of the method 200 shown in FIG. 2. The
exact order of the steps of the algorithm or method 500 shown in FIG. 5
is not required, and FIG. 5 shows only a high-level illustration of the
method 500. Steps may be reordered, steps may be omitted, and additional
steps may be included.

[0104] For illustrative purposes, the method 500 may be described with
reference to the elements and components shown and described in relation
to FIGS. 1 and 4 and may be executed by the control system described
herein. However, other components may be used to practice the method 500
and the claimed subject matter. Any of the steps may be executed by
multiple components within the control system.

[0105] Step 510: Start.

[0106] The method 500 may begin at a start or initialization step, during
which time the method 500 is monitoring operating conditions of the
vehicle and of the powertrain 100. Initiation may occur, for example, in
response to the vehicle operator inserting the ignition key, or initiate
may delay until called upon for a specific event, such as a vehicle
launch or gear change requested by the control system. The method 500 may
be configured to run on only a single loop or to run multiple times to
validate its results.

[0107] Step 512: Determine Heat Flux.

[0108] The method 500 determines the heat flux 154 being generated as a
result of the slipping event in the first clutch 132 or the second clutch
134. The heat flux 154 is determined as a function of the torque and slip
speed across the slipping clutch during the slipping event. Because the
heat flux 154 may be changing during the slipping event, if the method
500 is not looping numerous times during the slipping event, determining
the heat flux 154 may be repeated multiple times as part of each loop of
the method 500, or may be outputting determined heat flux 154
substantially constantly during the slipping event.

[0109] Step 514: Determine Grid Point Temperatures.

[0110] The method 500 determines the temperatures at the grid points
during the slipping event. As described herein, the temperatures may be
determined through equations modeling the heat flow into the first clutch
132 or the second clutch 134 during the slipping event. Determining the
grid point temperatures may also include choosing the number of grid
portions 135 to be used with the interface temperature model.

[0111] Step 516: Determine Interface Model Flux bulk temperature.

[0112] The method 500 determines the flux bulk temperature according to
the interface temperature model. The flux bulk temperature from the
interface temperature model is the average temperature of all of the
determined grid points. This flux bulk temperature is a relative bulk
temperature based only upon the heat flux 145 during the slipping event.

[0113] Step 518: Determine Delta Interface Temperature.

[0114] The method 500 determines the difference between the flux bulk
temperature from the interface temperature model (average of the seven
grid points) and the flux interface temperature (at grid point 1). This
differential is the delta interface temperature from the interface
temperature model. While the flux interface temperature model does not
determine the actual, or absolute, interface temperature of the first
clutch 132 or the second clutch 134 as a result of the heat flux 145, the
interface temperature model does determine the difference between the
flux bulk temperature and the flux interface temperature due to the heat
flux 145.

[0115] Step 520: Read Bulk Temperature from Thermal Model.

[0116] The method 500 determines or reads the absolute bulk temperature
from the five-state or the seven-state thermal model. The absolute bulk
temperature from the thermal model accounts for the temperature changes
caused by multiple slipping events and cooling periods over time, and
therefore provides a base point for determining the absolute interface
temperature from the delta interface temperature found by the interface
temperature model.

[0117] Step 522: Calculate Absolute Interface Temperature.

[0118] The method 500 calculates the absolute interface temperature using
both the interface temperature model and the five-state or seven-state
thermal model. The absolute interface temperature is calculated by adding
the absolute bulk temperature from the thermal model to the delta
interface temperature from the interface temperature model.

[0119] Step 524: Calculate Coefficient of Friction.

[0120] The method 500 will calculate the coefficient of friction for the
first clutch 132 or the second clutch 134 during the slipping event. The
coefficient of friction may be calculated in real time at each loop of
the method 500 or calculated as an average from multiple loops of the
method 500.

[0121] Step 526: Output Results.

[0122] The method 500 executes a control action with the results of the
interface temperature, such as outputting the results of the interface
temperature model for use in another calculation or by another process or
system. The results may include one or more of: the flux bulk
temperature, the flux interface temperature, the delta interface
temperature, the absolute interface temperature, the individual grid
point temperatures, and the coefficient of friction. Outputting the
results of the interface temperature model may include looping the method
500 if the slipping event continues.

[0123] The control system may store the absolute interface temperature and
other temperatures determined. Furthermore, the output of the interface
temperatures may be used by the control system to calculate maintenance
intervals or the predicted lifecycle of the second clutch 134 based upon
the absolute interface temperature experience during the slipping events
experience by the second clutch 134.

[0124] The detailed description and the drawings or figures are supportive
and descriptive of the invention, but the scope of the invention is
defined solely by the claims. While the best mode, if known, and other
embodiments for carrying out the claimed invention have been described in
detail, various alternative designs and embodiments exist for practicing
the invention defined in the appended claims.